Fixes #2491: Added support for using the same base class name of search model and data model in Gii [skip ci]

Fixes #1586: `QueryBuilder::buildLikeCondition()` will now escape special characters and use percentage characters by default

Moved file and path related methods from StringHelper to FileHelper, renamed StringHelper byte methods not to be misused as string methods

Appended newlines to every PHP document that did not have a newline as the last character in the file.